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  • 1
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    Springer
    Applied physics 34 (1984), S. 123-128 
    ISSN: 1432-0649
    Keywords: 42.55R ; 42.60D ; 42.65
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Pulse-shortening and pulse broadening effects in passively mode-locked lasers are analysed. A steady-state pulse duration limit is calculated and compared with round-trip simulations. The numerical calculations apply to a picosecond Nd: glass laser. Methods of short-pulse generation are discussed.
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  • 2
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    Applied physics 34 (1984), S. 171-173 
    ISSN: 1432-0649
    Keywords: 42.65 ; 42.80
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Interference of resonant ninth-order and nonresonant seventh-order nonlinear polarizations in Hg atoms has been studied, and direct conversion of fundamental ir radiation into the vuv has been obtained. The interference has been observed in the form of a Fano-Boitler contour. The efficiency of generation by ninth-order processes appears to be higher than that by seventh-order.
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  • 3
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    Applied physics 35 (1984), S. 77-82 
    ISSN: 1432-0649
    Keywords: 42.55 ; 42.65
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The coexistence of bistability and repetitive passive Q-switching of a CO2 laser with a gaseous saturable absorber has been investigated experimentally. With CH3F as the saturable absorber bistability has been observed simultaneously with passive Q-switching, whereas with CH3OH either one of these phenomena can only exist, as demonstrated for the first time. The measured features of both systems can be explained qualitatively by rate-equation theory.
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  • 4
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    Applied physics 33 (1984), S. 225-234 
    ISSN: 1432-0649
    Keywords: 42.65
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    Topics: Physics
    Notes: Abstract We have investigated two-photon resonant up conversion of 375 to 159 nm coherent radiation using the four-frequency process ω159=2ω375+ω1040 in cadmium vapour, where the ir component (1040 nm) is internally generated by the 375 nm pump tuned to the Cd two-photon transition 5s 2 1 S 0→5s6s 1 S 0. Scaling laws and tuning behaviour of both the 159 and 1040 nm output power were measured up to 1×108 W cm−2 pump intensity and 2×1017 cm−3 Cd number density. The results are compared to numerical calculations based on semiclassical theory in a stationary perturbation approximation up to third order. Here, in accordance with experimental results, the ir component was assumed to originate from a superposition of stimulated emission and parametric generation. The observed saturation effects turned out to be mainly due to population changes of the atomic levels involved and are qualitatively reproduced by calculations. Discrepancies with respect to absolute output levels are discussed in terms of the approximations in the theoretical formalism.
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  • 5
    ISSN: 1432-0649
    Keywords: 35.80 ; 42.65 ; 78.30
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The coherent excitation of molecular vibrations in liquids via off-resonant stimulated Raman amplification is shown to consist of two parts with vastily different spectral and temporal properties. One component situated at the frequency differenceω L −eω S of the driving fields follows almost instantaneously the system response function. The second part at the eigenfrequency eω 0 carries information on the vibrational dephasing. Detecting both frequency components simultaneously by coherent anti-Stokes probe scattering a novel 2-channel method is demonstrated. The vibrational dephasing time of thev 3-mode of CH3I is directly measured to beT 2=2.6±0.15 ps. This result gives experimental support to the deconvolution techniques required in conventional spectroscopy.
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  • 6
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    Applied physics 34 (1984), S. 69-72 
    ISSN: 1432-0649
    Keywords: 42.65
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    Topics: Physics
    Notes: Abstract Greatly improved second-harmonic emission has been obtained from dye monolayers adsorbed at quartz etalons. Two different types of interferometers have been studied in terms of the SH signal from dye coverage versus harmonic background emission. The phasematching-like conditions for constructive interferometric enhancement and the concomitant spatial and spectral emission characteristics are discussed in detail.
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  • 7
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    Applied physics 35 (1984), S. 149-153 
    ISSN: 1432-0649
    Keywords: 42.65 ; k
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The application of the resonant light pressure created by an axially symmetrical light field for collimating atomic beams has been considered. As an example, consideration is given to the possibility of collimating an atomic beam by the light field produced by the reflection of a plane wave from the internal surface of a metal cone. It has been shown that the radiation pressure can reduce the atomic-beam transverse velocities to the value of the order of 100 cm/s which corresponds to effective temperature of about 10−3 K. A method for producing collimated beams of cold atoms based on simultaneous deceleration and collimation of atomic beams by resonant laser radiation pressure is proposed.
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  • 8
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    Applied physics 62 (1996), S. 309-311 
    ISSN: 1432-0649
    Keywords: 52.40 ; 42.65
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The effects of the development of the three-wave phase on the amplitude of the pumping laser light, the scattered light, and the electron plasma wave are studied. Analytical solutions are obtained to describe a pumping laser light decreasing with time and the development of the electron plasma wave and scattered wave from an initial increasing state to saturation and finally to a decaying state which is closely related to the three-wave phase.
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  • 9
    ISSN: 1432-0649
    Keywords: 42.65
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report on an experimental and numerical investigation of the process of spontaneous optical vortices nucleation in a wave front of a laser beam passed through a photorefractive LiNbO3 : Fe crystal with self-induced nonlinear lens. The complex lens structure produces mainly defocusing of the beam passing through the crystal due to a negative variation of the refractive index, whereas side parts of the lens have a positive sign of refractive-index variation and partially focus the beam. The resulting wave-front distortions lead to a phase bifurcation occurring at a certain distance after the crystal when the amplitude of the light wave becomes zero. We study in detail the process of edge dislocation nucleation and its decay in the near field producing a pair of unity-charged opposite-sign screw dislocations. After birth, they spread along dislocation axes as stable objects.
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  • 10
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    Applied physics 63 (1996), S. 47-50 
    ISSN: 1432-0649
    Keywords: 31.20.Nt ; 42.65 ; 42.70
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Excited-State Absorption (ESA), Two-Photon Absorption (TPA) and the third-order polarizability γ(ω;ω,ω, − ω) have been investigated for a model dichloride derivative of a symmetrically substituted benzylidene analine (SBAC), using a multielectron configuration-interaction procedure. The calculations indicate that SBAC exhibits ESA across the visible region of the spectrum, but that it is not as extensive as for molecules such as the phthalocyanines. The magnitude of the third-order polarizability is dominated by resonance enhancement from a very strongA g →B u one-photon absorption. The calculated off-resonance value for γ(ω;ω,ω, − ω) suggests that SBAC is a potential candidate for ultrafast switching applications.
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  • 11
    ISSN: 1432-0649
    Keywords: 42.65 ; 51.70
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    Topics: Physics
    Notes: Abstract More than thirty rotational lines equally spaced by 587 cm−1 are generated simultaneously in the vicinity of the fundamental line by four-wave Raman mixing using a high-power picosecond Ti:Sapphire laser as a pump source and hydrogen as a Raman medium. Since the wavelength of this multifrequency laser emission extends from the near-infrared to the near-ultraviolet, it can be utilized as a tunable light source for picosecond spectroscopy. Because of the wide spectral bandwidth available, this procedure has great potential for the generation of ultrashort laser pulses by mode-locking these emission lines.
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  • 12
    ISSN: 1432-0649
    Keywords: 07.60 ; 42.65 ; 33.70
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A technique using a Fabry-Perot interferometer has been developed to calibrate high-resolution spectra obtained by Coherent Anti-Stokes Raman Spectroscopy (CARS). This technique was used to measure simultaneously the Raman frequency and the Raman signal at each laser shot. We demonstrate the accuracy of the method by measuring theQ(15) line shifts of molecular oxygen due to collisions with oxygen and water vapour.
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  • 13
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    Applied physics 34 (1984), S. 55-61 
    ISSN: 1432-0649
    Keywords: 42.65
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Transient parametric scattering is investigated theoretically using density matrix perturbation theory. Emphasis is placed on the effects of population and transverse or dephasing relaxation on the scattered parametric pulse durations. Pulse duration measurement provides important insight into the actual transient temporal behavior of four-wave mixing processes and is shown to be a potentially useful technique for the characterization of material time constants and incident pulse shape.
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  • 14
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    Applied physics 33 (1984), S. 51-56 
    ISSN: 1432-0649
    Keywords: 42.65 ; 78.20 ; 42.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A theoretical study is presented of a special case of stationary energy transfer in degenerate two-wave mixing in a reflection geometry. The two interacting beams consist of a beam and its first-order internal reflection component created at the boundary of a nonlinear medium. Numerical results obtained from the computer calculations are presented as graphs. It is found that, under suitable conditions, this phenomenon can be used to eliminate the multiple internal reflections.
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  • 15
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    Applied physics 33 (1984), S. 133-139 
    ISSN: 1432-0649
    Keywords: 33.80 ; 42.65
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Anti-Stokes Raman laser experiments using metastable atomic Tl and Sn have been performed. The required metastable population inversion is generated by photodissociation of TlI and SnBr2 with KrF laser radiation. The Tl(Sn) system permits frequency up-conversion by 7793 cm−1 (17,163 cm−1). By optimization of system parameters, uv output energies up to 2.5 mJ (377 nm) and conversion efficiencies of more than 25% have been achieved for Tl. Further improvements and principal limitations will be discussed.
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  • 16
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    Applied physics 34 (1984), S. 107-122 
    ISSN: 1432-0649
    Keywords: 42.65 ; 71.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A short review on the theoretical description of nonlinear optical phenomena which are caused by an electric polarization cubic in the electric field amplitudes is given. Then the microscopic theories for the calculation of the nonlinear susceptibility, especially in semiconductors, are briefly reported. After a short section on the bandstructure of IV–VI compounds in a magnetic field, the lineshapes of the coherent anti-Stokes radiation as a function of the magnetic field are discussed in detail. In the experimental part measurements of coherent anti-Stokes Raman scattering (CARS) in PbTe and PbSe epitaxial films are reported. We observed pure as well as combined spin flip transitions. These data and the results of additionally observed interbandtransitions were used in least squares fits and consistent sets of bandparameters of PbTe and PbSe were obtained.
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  • 17
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    Applied physics 35 (1984), S. 59-64 
    ISSN: 1432-0649
    Keywords: 42.65
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    Topics: Physics
    Notes: Abstract The observation of chaos in a hybrid optical bistable device is reported. There is no delay line in this system. An investigation of the mechanism concentrates on a somewhat simplified structure. This structure is described by a third-order differential equation with quadratic nonlinearity. Its realization as an electronic circuit is studied in detail. As we observe patterns of universal behaviour, we also comment on the relation to iterative maps.
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  • 18
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    Applied physics 26 (1981), S. 67-72 
    ISSN: 1432-0649
    Keywords: 42.65
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    Topics: Physics
    Notes: Abstract Polarization decay in the presence of a standing electromagnetic wave field at a Doppler broadened transition is investigated theoretically and experimentally. It is shown that in the direction opposite to the propagation of an excited pulse the polarization decays at a transition frequency rather than at an exciting field frequency as usual. This permits the use of transients both in studies of relaxation processes and in Doppler-free super-high resolution spectroscopy. A resonant coherent transient has been used in measurements of relaxation decay constants of a dipole moment for collisions in SF6 (λ=10.6μm). This method has enabled one to resolve reliably the structure of theQ(38) transition (λ=10.6μm) of theF 1 0 +E 0=F 2 0 line of the 0→v 3 band in SF6 within a Doppler absorption line.
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  • 19
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    Applied physics 26 (1981), S. 105-110 
    ISSN: 1432-0649
    Keywords: 42.65
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    Topics: Physics
    Notes: Abstract We present an analysis of the impulse response of four-wave mixing, in the case where the “two-photon term” of the nonlinear susceptibility is dominant. The nonlinear interaction itself will be considered to be steady state. The conditions of negligible pump depletion are considered first. It is shown that the reflected beam has only the character of perfect phase conjugation if the pulse length is longer than the medium length, and the latter is short compared to the characteristic distance of the problem. The “weak-pulse” approximation involving only two coupled equations is compared to the exact four-wave solution, when the medium thickness approaches the critical oscillation threshold. Finally, the stability and existence of steady-state solutions is analyzed for very long media (compared with the oscillation length).
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  • 20
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    Applied physics 33 (1984), S. 161-165 
    ISSN: 1432-0649
    Keywords: 42.65 ; 78.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Wavefront reflectivity in a conventional degenerate four-wave mixing (FWM) configuration can be calculated, using either approximate formulae, or exact numerical methods to solve the nonlinear coupled-wave equations. We have computed the wavefront reflectivity for FWM in a transmission and reflection geometry, respectively, using these two different methods. A comparison between them indicates that these formulae are reasonable approximations when beam coupling, diffraction efficiency and absorption are all low, and especially in the case of transmission geometry.
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  • 21
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    Applied physics 35 (1984), S. 17-21 
    ISSN: 1432-0649
    Keywords: 42.70 ; 42.65 ; 42.80
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Anisotropic selfdiffraction in BaTiO3 crystals utilizing the large electrooptic coefficientr 42 is described. In the absence of an external electric field the generated space charge field is determined by diffusion processes. The theory is in agreement with the experimental results. The angles between extraordinary and ordinary beams, the intensity and time dependence of transmitted and diffracted beams, and phase conjugation effects are measured and evaluated.
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  • 22
    ISSN: 1432-0649
    Keywords: 42.65 ; 33.20
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    Topics: Physics
    Notes: Abstract Thermometry of an oxy-acetylene flame using multiplex Degenerate Four-Wave Mixing (DFWM) of C2 is demonstrated. More than 100 rotational transitions in thed 3 Π g ←a 3 Π u (0,0) Swan band of C2 could be recorded simultaneously by use of a pulsed, broad bandwidth “modeless” laser. Temperatures were inferred by fitting temperature-dependent synthetic spectra of single- or multiple-shot averaged spectra. The strength and reliability of recorded signals together with the large number of rotational lines observed suggest that multiplex DFWM is a promising technique for minor species detection and for temporally resolved temperature measurements in luminous environments. Factors influencing the accuracy and precision of single-shot thermometry using the technique are discussed.
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  • 23
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    Applied physics 62 (1996), S. 479-483 
    ISSN: 1432-0649
    Keywords: 78.30 ; 78.32 ; 42.70 ; 42.65
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A design of a compact blue-green stimulated Raman shifter pumped by the third harmonic of a Nd:YAG laser is presented. Design parameters given here are based on our experimental investigation of various optimization techniques involving parametric studies. Blue-green energy conversion of up to 66% is achieved. The problem of optical breakdown is addressed.
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  • 24
    ISSN: 1432-0649
    Keywords: 36.40 ; 42.65
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    Topics: Physics
    Notes: Abstract The hot luminescent reaction zones of CO2-laser-induced pyrolysis flames using SiH4/C2H2 gas mixtures with different silane to acetylene ratios and with and without diborane additives were investigated by means of H2 Q-branch CARS spectroscopy, leading to spatial temperature profiles in gas flow direction. In the case of B2H6 additive to the stoichiometric SiH4/C2H2 mixture a high temperature plateau (≈ 800–1000 K) of the reactant gas volume develops already several millimetres before reaching the CO2-laser focus line. This precursor preheating zone could be explained by the catalytic effect of boron atoms or boron-containing intermediate species in the flame. A similar behaviour for acetylene-rich flames operating at half laser power was not observed.
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  • 25
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    Applied physics 63 (1996), S. 145-150 
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    Keywords: 42.65
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    Topics: Physics
    Notes: Abstract Guiding of multiple signal beams in an induced all-optical cable is studied theoretically. A balance relation is derived for the interaction geometry and undistorted propagation of bright elliptical signal beams nested in a single ring dark soliton. The numerical analyses show a remarkable misalignment stability of the parallel guiding scheme.
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  • 26
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    Applied physics 63 (1996), S. 117-120 
    ISSN: 1432-0649
    Keywords: 42.60B ; 42.60D ; 42.65
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    Topics: Physics
    Notes: Abstract Narrow linewidth, single spectral mode operation has been obtained in a high power, 810 nm broad-area diode laser in an extended cavity configuration with a grating as external reflector (grating feedback). For stable operation it was necessary to misalign the feedback slightly in the plane of the laser junction. Characteristics of the thus obtained laser system are a linewidth below 5 MHz, an output intensity of about 50% of the free running power, a large-scale tuning range of 15 nm and continuous scanning over 4 GHz. In the spatial domain, the laser remains multimode and astigmatic. To show the practical applicability of this system, saturated absorption of a krypton line is demonstrated.
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  • 27
    ISSN: 1432-0649
    Keywords: 33.00 ; 42.55 ; 42.65
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    Topics: Physics
    Notes: Abstract The effect of Mid-InfraRed (MIR) (λ ≅ 12 μm) and Far-InfraRed (FIR) (λ ≽ 100 μm) emission from excited ammonia on the absorption of intense radiation of a TEA CO2 laser has been studied experimentally under collisional and collisionless excitation conditions with ammonia pressures from 0.5 to 0.03 Torr. The energy of MIR and FIR emission was studied as a function of NH3 pressure and laser energy fluence. Particular emphasis was given to the kinetics of MIR and FIR emission generation at different NH3 pressures and to the measurement of the time delay of re-emitted pulses relative to the exciting CO2 laser pulse. It has been found that the re-emission in the MIR range is highly collisional in nature. The intensity of MIR emission drops sharply (asp 3) with decreasing NH3 pressure and its delay time relative to the exciting laser pulse increases. At the same time, re-emission in the FIR range (in the case of resonant excitation of NH3 at the 9R (30) line of CO2 laser) is observed during an exciting pulse up top 〈 0.03 Torr. When binding the rotational sub-levels of a molecule with transitions, FIR emission acts as rotational relaxation and thus leads to an increase in NH3 IR absorption even at collisionless excitation.
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  • 28
    ISSN: 1432-0649
    Keywords: 7.65 ; 33.00 ; 42.60 ; 42.65 ; 42.80
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    Topics: Physics
    Notes: Abstract A new widely tunable source in the infrared for use in high-resolution spectroscopy and trace-gas detection is described. This spectroscopic source is based on Difference Frequency Generation (DFG) in gallium selenide (GaSe) and is continuously tunable in the 8.8–15.0 μm wavelength region. Such a DFG source operates at room temperature which makes it a useful alternative to a lead-salt diode-laser- based detection system that requires cryogenic temperatures and numerous individual diode lasers.
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  • 29
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    Applied physics 62 (1996), S. 59-64 
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    Keywords: 42.60 ; 42.65 ; 78.30
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    Topics: Physics
    Notes: Abstract To investigate the full conversion of pump power to the Stokes waves in stimulated Raman scattering with a single-pass cell, unconverted pump energies have been analyzed in detail in relation to the first Stokes, second Stokes and first anti-Stokes energies. Adoption of a long focusing configuration with a high-pressure cell was found to be effective but insufficient to suppress the four-wave mixing effect, because a small amount of pump energy always remained undepleted. Comparison of the results using pump beams of various spectral and spatial mode characteristics from alexandrite and Nd:YAG lasers revealed that the spatial mode quality was the most critical parameter for full depletion of a pump pulse.
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  • 30
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    Applied physics 62 (1996), S. 139-142 
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    Keywords: 42.65
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    Topics: Physics
    Notes: Abstract A four-frame technique for interferogram analysis is used to measure the transverse phase distribution of nonlinearly split 2D dark beams. Pairs of diametrical phase shifts within each ring are retrieved from the experiment. This result is one of the tests required to denote the formations observed as ring dark solitons.
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  • 31
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    Applied physics 62 (1996), S. 293-297 
    ISSN: 1432-0649
    Keywords: 42.10 ; 42.65 ; 42.70
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    Topics: Physics
    Notes: Abstract Fluence dependence of transmission in three dyes, viz. indanthrone, dichloroindanthrone and violanthrone, is reported at 532 nm as well as at 1.06 µm. These dyes show optical limiting at both these wavelengths for nanosecond pulses. The limiting is due to the combined effect of reverse saturable absorption from the triplet state and thermal defocussing in the dye solutions.
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  • 32
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    Topics: Physics
    Notes: Abstract We report the observation of coherent uv emission at 330.2±0.5 nm when sodium vapor in a heatpipe is irradiated with a pulsed visible dye laser with output wavelength in the 570–595 nm region. It is found that intense uv emission can be produced from Na atoms as well as from Na2 molecules. The excitation functions and their dependence on vapor density and laser power density are presented and the mechanisms for producing the emission are discussed.
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  • 33
    ISSN: 1432-0649
    Keywords: 33.10 ; 42.65
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    Topics: Physics
    Notes: Abstract The accuracy and precision of oxygen concentration and temperature measured by dual-broadband rotational Coherent Anti-Stokes Raman Spectroscopy (CARS) were investigated in nitrogen-oxygen mixtures at atmospheric pressure and temperatures between 290 and 1410 K. The relative standard deviation of temperatures evaluated from pure oxygen rotational CARS spectra was found to be around 5%, and the mean temperature was the same as for nitrogen CARS spectra, except for temperatures above 1000 K, where the temperature was 120 K below the correct value. The in situ calibrated oxygen concentrations were within 10% of the correct value, with a standard deviation of around 1.2% for the mixtures of 12 and 20% oxygen in nitrogen. For the lowest oxygen concentrations considered in this study (2 and 4%), the systematic errors in the evaluated concentrations were very large, and the standard deviation of repeated single-shot measurements was above 2%. However, employing weighting in the spectral fitting routine reduced the errors in the concentration and the single-shot standard deviation was lowered to 0.5%. Finally, it was shown that spectral interference (from oxygen) in a rotational CARS spectrum of nitrogen generally had little impact on the temperature evaluated from fitting the spectra to theoretical nitrogen spectra.
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  • 34
    ISSN: 1432-0649
    Keywords: 42.30 ; 42.65 ; 42.70 ; 42.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Degenerate Four-Wave Mixing (DFWM) based on excited-state absorption in azo-dye doped polymer films is firstly reported. Under a pre-exciting argon laser at 514.5 nm, DFWM is performed using a 632.8 nm HeNe laser which is absorbed only slightly when the molecules are in the ground state. The dynamic behavior of the DFWM signal due to excited-state absorption is also treated theoretically.
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  • 35
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    Applied physics 62 (1996), S. 389-397 
    ISSN: 1432-0649
    Keywords: 02.60.Cb ; 02.70.-c ; 42.10 ; 42.25.Bs ; 42.65
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    Topics: Physics
    Notes: Abstract We describe and example the Beam Propagation Method (BPM) used to model and simulate nonlinear refractive and absorptive effects in materials with applications to optical limiting and switching. Various scenarios including laser-beam trapping and laser-beam division are investigated, in order to demonstrate the power of the BPM. A novel technique is also described for efficiently modelling the external far-field propagation from nonlinear media, including the propagation of non-Gaussian-shaped spatial profiles. The methods are finally combined with the phenomenon of nonlinear absorption to demonstrate enhanced power limiting in the presence of self-refraction. Optimal parameters for high-fluence power-limiting are subsequently discussed.
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  • 36
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    Notes: Abstract We show that using the approximation of fixed intensity analytical formulae, describing the process of induced phase modulation for the beams involved in second-order nonlinear optical processes can be derived. Expressions that allow the optimization of the phase shifts experienced by the fundamental and generated waves are presented for nonlinear quadratic processes, second-harmonic generation and sum-frequency mixing. In the case of seeding at the generated wavelength, the phase shift of the fundamental wave is due to two interactions: (i) a cubic one, based on coupled second-order processes (cascade cubic nonlinearity) and (ii) single quadratic interaction with participation of the seeding wave. By comparison with the exact numerical solution, we defined the input parameters of the beams for which this analytical approach is valid. It is shown that phase shifts exceeding π/2 can be correctly predicted using the expressions obtained.
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  • 37
    ISSN: 1432-0649
    Keywords: 07.62 ; 42.65
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    Topics: Physics
    Notes: Abstract Mixing experiments with 30 THz CO2-laser radiation as well as the detection of 35 ps 30 THz pulses of an optical-free-induction-decay CO2-laser system have been performed with the first nanometer thin-film Ni-NiO-Ni diodes with a minimum contact area of 0.012 µm2. Difference frequencies up to 85 MHz were detected by mixing two different CO2-laser beams coupled to the diode with an integrated bow-tie antenna. The dependence of the beat signal on bias voltage, laser power and polarization of the infrared laser radiation was determined.
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  • 38
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    Applied physics 63 (1996), S. 161-166 
    ISSN: 1432-0649
    Keywords: 42.20 ; 42.30 ; 42.65
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    Topics: Physics
    Notes: Abstract The field, the propagation and the imaging characteristics of two Gaussian optical beams with orthogonal polarization passing through a family of Kerr-law nonlinear shifted parabolic graded-index rod lenses are investigated. The coupled differential equations of the dimensionless beam-width parameters of two Gaussian optical beams are derived by using a variational approach and then solved. It is concluded that there are two regimes of propagation and that the power, the incident waist radius and the position of one beam have large effects on the field, the propagation and the imaging characteristics of the other beam.
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  • 39
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    Applied physics 63 (1996), S. 237-242 
    ISSN: 1432-0649
    Keywords: 42.55 ; 42.65 ; 42.70
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    Topics: Physics
    Notes: Abstract We experimentally studied properties of traveling-wave excitation and traveling-wave pulse compression for a Nd : glass laser system with a streak camera. These properties were extended to second-harmonic generation with a type-11 KDP crystal. We found that the second-harmonic pulse generated from the chirped-fundamental pulse also has a good chirp linearity, but the spectral bandwidth and temporal duration were reduced. We demonstrated the effective subpulse suppression in the compressed pulse with the second-harmonic generation. The pulse with tilted wave front, short wavelength and high contrast ratio can be obtained by the second-harmonic generation of traveling-wave pulse.
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  • 40
    ISSN: 1432-0649
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    Topics: Physics
    Notes: Abstract It is shown that the system polarizer-frequency-doubling crystal(s)-analyzer has a nonlinear transmission for the fundamental wave. The intensity-dependent transmission of this device is due to the nonlinear phase shift that the fundamental beam obtains in the nonlinear crystal as a result of cascaded second-order processes. Depending on the mutual orientation of the polarizer and the analyzer such effects as self-induced transparency and self-induced darkening can be realized.
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  • 41
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    Applied physics 63 (1996), S. 537-540 
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    Keywords: 42.65 ; 42.60
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    Topics: Physics
    Notes: Abstract We experimentally demonstrate vector phase conjugation in Cr4+:YAG saturable absorber at 1.06μm with nanosecond pulses using degenerate four-wave mixing with linearly-polarized pump beams of arbitrary strengths. The experimental results show that the phase conjugate wave produced by this method can correct depolarisation induced by a birefringent medium.
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  • 42
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    Applied physics 63 (1996), S. 599-604 
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    Keywords: 42.40 ; 42.65 ; 42.70
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    Topics: Physics
    Notes: Abstract We investigate holographic scattering processes in BaTiO3 pumped by two coherent copropagating waves. Four lines are observed on a screen behind the sample. The experimental results are well described by a model taking into account parametric mixing of four copropagating waves and limitations of optically induced space charge fields because of the finite trap density.
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  • 43
    ISSN: 0340-3793
    Keywords: PACS: 42.40 ; 42.65 ; 42.70
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    Topics: Physics
    Notes: Abstract.  A generalized systematic description of the Two-Wave Mixing (TWM) process in sillenite crystals allowing for arbitrary orientation of the grating vector is presented. An analytical expression for the TWM gain is obtained for the special case of plane waves in a thin crystal (∣g∣d≪1) with large optical activity (∣g∣/ϱ≪1, g is the coupling constant, ϱ the rotatory power, d the crystal thickness). Using a two-dimensional formulation the scope of the nonlinear equations describing TWM can be extended to finite beams in arbitrary geometries and to any crystal parameters. Two promising applications of this formulation are proposed. The polarization dependence of the TWM gain is used for the flattening of Gaussian beam profiles without expanding them. The dependence of the TWM gain on the interaction length is used for the determination of the crystal orientation. Experiments carried out on Bi12GeO20 crystals of a non-standard cut are in good agreement with the results of modelling.
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  • 44
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    Keywords: 42.65 ; 78.20 ; 42.40
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    Notes: Abstract A detailed analysis is given of the properties of the algebraic equations obtained when solving directly the nonlinear coupled-wave equations for degenerate two-wave mixing in a reflection geometry. An efficient method is developed for computing the appropriate root only amongst the multiple roots of these algebraic equations.
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  • 45
    ISSN: 1432-0649
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    Notes: Abstract Using a new seventh-order numerical method [theO(h 7) method] for solving two-point boundary value problems, numerical solutions of the first-order nonlinear coupledwave equations for degenerate two-wave and four-wave mixing in a reflection geometry have been obtained. A computer program employing the Gauss-Jordan elimination technique has also been adopted to effectively solve the resultant large, sparse and unsymmetric matrix, obtained from theO(h 7) method and the Newton-Raphson iteration method. Numerical results from the computer calculations are presented graphically. A comparison between thisO(h 7) method and the shooting method, mainly from the viewpoint of computational efficiency, is also made.
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  • 46
    ISSN: 1432-0649
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    Topics: Physics
    Notes: Abstract Resonant nonlinear four-wave mixing processes have been studied in sodium vapor. The generation of cw uv radiation and the upconversion of λ=10.8 μm light is reported. The coefficientC=P 4/P1P2P3 obtained was on the order of ∼10−2 W−2, the pump spectral width being 12GHz. Resonant atomic nonlinearities are shown to be used for effective cw frequency conversion.
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  • 47
    ISSN: 1432-0649
    Keywords: 42.65 ; 32 ; 33
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    Topics: Physics
    Notes: Abstract The general steady-state solution of the density matrix equations for a Doppler broadened three-level system irradiated by two resonant standing-wave laser beams of arbritrary intensity is analyzed. The solution is expressed in a matrix continued fraction form, that involves 4×4 matrices in important configurations and is convenient for numerical computations. Some representative cases including the absorption spectra for a probe laser of arbitrary intensity, the Doppler-free multiphoton resonances and the optically pumped lasers are analyzed numerically in connection with previous experimental investigations.
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  • 48
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    Applied physics 16 (1978), S. 47-57 
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    Keywords: 32 ; 42.65
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    Notes: Abstract Analytical results have been obtained for some aspects of polyatomic molecular interaction with resonant ir laser radiation. The following effects are investigated by use of Schrödinger's equation solution for natural multilevel models: the role of dynamic Stark effect in the transient region from molecular low levels to the quasi-continuum of highly excited vibrational levels; broadening of multiphoton transitions because of relatively fast decay into the quasi-continuum; threshold excitation property of multilevel systems with random detunings. Possible applications to constructing models for numerical calculations dealing with the molecule excitation problem are discussed.
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  • 49
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    Applied physics 20 (1979), S. 291-294 
    ISSN: 1432-0630
    Keywords: 42.65 ; 82.50
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    Notes: Abstract Two photon excitation by a tunable dye laser is used to determine the decay kinetics of some aliphatic tertiary amines. The feasibility of obtaining laser action from trimethylamine and triethylamine by KrF laser pumping is quantitatively discussed.
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  • 50
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    Applied physics 17 (1978), S. 151-154 
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    Keywords: 33 ; 42.65
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    Notes: Abstract Lines of theQ-branch of vibrational rotational spectra are distinguished fromP(R)-lines by light induced anisotropy in absorbing gases. We report, for the first time, on experiments using a linearly polarized saturation beam. A CO2-laser was employed to investigate the molecule SF6.
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  • 51
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    Applied physics 17 (1978), S. 199-201 
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    Keywords: 32 ; 42.65
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    Notes: Abstract Lamb-dips have been observed in the weak calcium intercombination line by monitoring resonance fluorescence in an atomic beam excited by light of a stabilized cw dye laser inside or outside the laser cavity. A highly sensitive detection scheme is described.
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  • 52
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    Applied physics 24 (1981), S. 71-84 
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    Keywords: 32 ; 42.65
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    Notes: Abstract We consider cooling of a trapped particle in the limit when the position and velocity variables do not change adiabatically. The slowly varying quantity in a harmonic trap is then the energy, and a representation based on oscillator eigenstates is used. For large excitation, fast particles, a Fokker-Planck expansion is obtained which is valid when our adiabatic description breaks down. Estimates of the initial cooling rate are given and compared with earlier results. Our treatment requires a large number of oscillator states to be coupled by each one-photon process, and in this limit the diffusion will make the expansion invalid towards the end of the cooling; our physical interpretation is that particles leak out of the trap. The opposite case, the Lamb-Dicke regime, is advantageous for cooling experiments, and then a difference equation replaces the Fokker-Planck equation of the present paper.
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  • 53
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    Applied physics 33 (1984), S. 227-230 
    ISSN: 1432-0630
    Keywords: 42.40 ; 42.65
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    Notes: Abstract It is shown that dynamical hologram formation in photorefractive, optically active crystals is accompanied by polarization and energy exchange. These effects may be used like new effective holographic methods for determinations of crystal parameters and optical signal processing in real time. In self-diffraction a polarization rotation the order of degrees/cm for Bi12TiO20 and Bi12SiO20 is predicted.
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  • 54
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    Applied physics 62 (1996), S. 143-149 
    ISSN: 1432-0630
    Keywords: 61.80 ; 42.70 ; 42.65
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    Notes: Abstract Intensity-dependent absorption of 25 ns excimer laser pulses in common UV-window materials was investigated. By employing a calorimetric technique which provides greatly enhanced sensitivity compared to transmissive measurements, two-photon absorption coefficients were determined at intensities of 2–80 MW/cm2 and found to be in good agreement with previous measurements at 10–100 GW/cm2. Also, color-center formation in fused silica was observed. It was possible to quantify transient and cumulative effects as a function of intensity.
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  • 55
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    Applied physics 13 (1977), S. 159-163 
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    Keywords: 42.65 ; 32
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    Notes: Abstract Two-photon resonant four-wave mixing has been studied both theoretically and experimentally. Tunable infrared radiation between 2 and 20 μm has been generated in potassium and caesium vapours. The mixing efficiency is found to be severely limited by competition with Raman scattering.
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  • 56
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    Applied physics 13 (1977), S. 271-280 
    ISSN: 1432-0630
    Keywords: 32.20 ; 42.10 ; 42.65
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    Notes: Abstract This paper analyses effects related to the real part of the gaseous electric susceptibility in microwave-microwave and infrared-microwave double resonance experiments on two transitions with a common level. The most interesting features are obtained when the gaseous refractive index is probed far off resonance, i.e. in the tail of the dispersion characteristic and when the pump frequency is scanned around the resonance: a resonant change of the refractive index for the probe field is observed, the shape of which is that of the saturated pump line. A calculation using a model of strong collisions gives results in good agreement with the experimental ones. Applications of these phenomena to the determination of frequencies and transition matrix elements of infrared lines are discussed in the general case of lack of overlapping of the laser gain profile and of the infrared line. It is proposed to use these dispersion effects to detect Doppler-free infrared two-photon molecular absorption.
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  • 57
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    Applied physics 14 (1977), S. 65-77 
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    Keywords: 42.65
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    Notes: Abstract We have studied experimentally self-focusing of light in the liquid crystalline mediump-ethoxybenzyldine-p-butylaniline (EBBA). By variation of temperature, the response time of the field-induced refractive index was adjusted from larger than to smaller than theQ-switched laser pulsewidth. Accordingly, self-focusing varied from transient to quasi-steady-state. The results agree well with existing theoretical predictions and can be qualitatively understood from a simple physical description. The induced stimulated Brillouin scattering was also measured and was shown to be responsible for the limiting diameter of the self-focused beam in the present case.
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  • 58
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    Applied physics 15 (1978), S. 209-211 
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    Notes: Abstract Continuous coherent radiation in a gas observed in a spacially separated standing wave fields is reported for the first time. The radiation was observed in the center of lineF 2 (2) in methane at the interaction of atoms with two standing waves separated by the distance of 3.5 cm.
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  • 59
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    Applied physics 15 (1978), S. 219-222 
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    Notes: Abstract The paper investigates the observation of coherent radiation in separated fields for the case of two-level atoms. The coherent radiation is due to polarization transfer at large distances. The Doppler phase angle is cancelled due to a phase jump at the nonlinear interaction of the fields with the atoms. A peak in intensity with a width inversely proportion to the flight time arises at the line center.
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  • 60
    ISSN: 1432-0630
    Keywords: 42.65 ; 32
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    Notes: Abstract Coherent radiation at 89.6 nm has been obtained through third-harmonic conversion of the 268.8 nm pulses in mercury vapors. Tunability of the fourth-harmonic frequency of the Nd: glass laser radiation to the 6s 1 S 0–8s 1 S 0 double quantum resonance of Hg atoms has been used for the resonant enhancement of the twelfth-harmonic output. Possibility to phase match the generated radiation and driving polarisation in pure vapors without employing of bufer gas has been demonstrated.
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  • 61
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    Applied physics 15 (1978), S. 439-450 
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    Keywords: 42.55 ; 42.65
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    Notes: Abstract A theoretical model for the ultrashort-pulse (USP) generation by lasers with saturable absorbers is presented. The gain medium is assumed to be a two-level system whereas the absorber is described by a four-level system which is characterized by a two-stage absorption process and the pertinent relaxation times. Laser dynamical equations are developed in the rate-equation approximation and boundary conditions appropriate for an unidirectional ring cavity are established. Evolution of USP is investigated for different combinations of parameter values appropriate for solid-state laser systems by computer simulation, employing a finite difference approximation for the dynamical equations. It is shown that USP output is attainable even if the cross-section of the excited-state absorption isgreater than that of the ground-state absorption and the laser is operating just above threshold. In fact, it is found that through the participation of a strong excited-state absorption the discrimination against satellite pulses is enhanced so that single-pulse output is more achievable. Furthermore, it is proposed that single picosecond pulses may be obtainable from relatively broad initial peaks by utilizing the high pulse-selection and pulse-shortening efficiency of the absorber due to the contribution of the excited-state absorption. The applicability of the present model to singlet-triplet crossing and photoisomer formation is also discussed.
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  • 62
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    Applied physics 16 (1978), S. 235-237 
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    Keywords: 32 ; 42.65
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    Notes: Abstract J-dependence of intensity-dependent polarization change of the elliptically polarized light in atomic resonance lines is studied both theoretically and experimentally.
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  • 63
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    Applied physics 16 (1978), S. 151-154 
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    Keywords: 42.65 ; 42.55 ; 33
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    Notes: Abstract We observed tunable UV radiation down to 175 nm by SRS of the output of a frequency-doubled dye laser in H2. The high power output of the 4th anti-Stokes to 5th Stokes line generated by the frequency doubled dye laser and the 8th anti-Stokes to 3rd Stokes line generated by the undoubled dye laser represents a broadly tunable coherent radiation source between 189 nm and 2064 nm.
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  • 64
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    Applied physics 18 (1979), S. 195-198 
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    Keywords: 33.20F ; 42.65
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    Notes: Abstract Coherent Stokes Raman spectra of the ν1 and ν3 bands of CH4 have been recorded in mixing two pulsed lasers (ruby and dye) of very good spectral and spatial quality. The results show a resolution of about 0.010 cm−1 for a 10 Torr pressure, corresponding in great part to Doppler broadening.
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    Applied physics 15 (1978), S. 213-218 
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    Notes: Abstract The Wiener functional expansion method for the analysis of nonlinear systems is applied to identify and analyze both nonlinear and linear molecular systems by spectroscopic methods. As the sampling filter (monochromator) of any spectroscopic apparatus may be defined by a Weber-Hermite polynomial, an analysis of the refracted or scattered light by orthogonal polynomials is easily achieved. Time averaging obtains the Weber-Hermite coefficients which permit the characterization of the molecular system with respect to the polarization of the incident and scattered light. In the case of two series of measurements made with incident and emerging light polarized in different directions: the identification of the JonesM matrices for the molecular system irradiated is possible. In the case of three series of measurements made, for example, with incident and emerging light (a) circularly polarized corotating, (b) circularly polarized contrarotating, and (c) plane polarized perpendicular: the identification of the molecular system's McClain invariants related to the vibrational symmetry group for Raman inelastic light scattering is possible. The analysis presents a unified picture of elastic and inelastic light scattering and one-photon and two-photon processes. The apparatus described would detect those instances in molecular systems for which Beer's law does not apply.
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    Applied physics 17 (1978), S. 53-62 
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    Keywords: 42.10 ; 42.65
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    Notes: Abstract The coherent interaction of short optical pulses with a nonlinear active resonant medium is calculated. The rigorous and self-consistent solution of the coupled nonlinear Maxwell-Bloch equations including transverse and time-dependent phase variations predicts the onset on an on-resonance self-focusing that agrees very well with a previous perturbation treatment and with recent experiments in sodium and neon. The formation of this dynamic self-action effect is elucidated as being due to the combined effects of diffraction and the inertial response of the active media. Accuracy and computational economy are achieved simultaneously by redistributing the computational grid points according to the physical requirements of the problem. Evenly spaced computational grids are related to variable grids in physical space by a range of stretching and rezoning techniques including adaptive rezoning where the coordinate transformation is determined by the actual physical solution.
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    Applied physics 17 (1978), S. 73-77 
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    Notes: Abstract The effect of self-focusing of a high-power light beam with an elliptical cross-section in a strongly ionised plasma has been evaluated. The mechanism of self-focusing considered is non-uniform heating of plasma by an electromagnetic wave having transverse variation of amplitude along its wave front. The heating causes redistribution of carriers which lead to a nonlinear relationship between the electron density and the electric vector and hence to a field-dependent effective dielectric constant. It is found that the beam gets focused at different focal points in different directions exhibiting the effect of astigmatism. There are several critical powers, below thex=0,y=0 planes; at higher powers one dimension focuses while the other defocusses, an oscillatory waveguide is formed in both dimensions. Above the highest critical power both dimensions self-focus, the dimensionless beam width parametersf 1 andf 2 forx andy focusing reach different minima corresponding to different self-focusing distances beyond which both dimensions continue diverging. The effect of energy loss through absorption from the beam has also been considered. It has been observed that absorption brings about a reduction in the extent of self-focusing and favours defocusing of the beam.
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    Applied physics 24 (1981), S. 119-120 
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    Notes: Abstract A technique of fast deep cooling of atomic or molecular buffer gases by laser radiation is proposed. With Na vapor as a cooling agent interacting with a laser field a cooling time of about 10−3s and minimum temperature of about 25K can be attained.
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    Applied physics 20 (1979), S. 287-290 
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    Notes: Abstract The cross-sections of excited-state absorption have been measured for several tertiary amines. The high values found explain the unsuccessful attempts to obtain laser action in KrF-laser pumped vapors of tertiary amines.
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    Notes: Abstract The noise characteristic of available laser sources limits the sensitivity of many types of nonlinear spectroscopy. We show how to maximize the sensitivity by optimizing the strength of a local oscillator wave in a heterodyne detection scheme without altering the amplitude of the wave being detected. The intensity profile of the optimum local oscillator closely matches that of the incident probe wave, but the optimum intensity is much less than that of the probe under realistic conditions. A general signal-to-noise analysis applicable to all nonlinear spectroscopy techniques is presented along with specific applications to coherent Raman spectroscopy, two-photon absorption, saturation spectroscopy, and optical coherent transient techniques. A simple optimization procedure employing polarization selection rules is described. Detailed calculations are performed for the case of TEM00 waves interacting via a third-order nonlinear susceptibility and for the case where the sample is simultaneously probed at many different frequency combinations.
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  • 71
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    Applied physics 24 (1981), S. 89-106 
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    Keywords: 33 ; 42.65 ; 82.50
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    Notes: Abstract A review of laser-induced photoionization of polyatomic molecules and the application of this process in mass-spectrometry is presented. Combination of laser selective photoionization and mass spectral analysis of fragments as a promising tool for the detection of trace amounts of complex molecules is considered particularly.
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  • 72
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    Applied physics 24 (1981), S. 349-355 
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    Notes: Abstract We construct field equations and generalised Bloch equations for multiphoton processes involving the coherent interaction of a number of distinct electric fields with an arbitrary number of atomic eigenstates, and apply the equations to some physical examples. Transient stimulated hyper-Raman scattering, in the low-conversion regime and far from saturation, has been studied analytically. Assuming that the pump pulse interacts with the medium byn-photon absorption, we find expression for the intensity of the generated Stokes pulse.
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  • 73
    ISSN: 1432-0630
    Keywords: 42.60 ; 42.65
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    Notes: Abstract In this paper we describe the construction of a monochromatic and frequency stabilized continuous wave (cw) source in the 5 μm region. It is built up by a cw single line, single-mode frequency and amplitude stabilized CO2 laser. This primary CO2 laser source is then frequency-doubled in a tellurium crystal using second harmonic generation (SHG). The obtained emission is monochromatic (half-width 50 kHz). The frequency can be varied discreetly from 4.6 μm to 5.5 μ depending on the CO2 laser line chosen.
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  • 74
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    Applied physics 24 (1981), S. 11-12 
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    Keywords: 42.65 ; 07.65 ; 33.90
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    Notes: Abstract Experimental observation of optical Ramsey interference in saturated absorption of methane in a low-pressure gas cell with three spacially separated laser beams at 3.39 μm is reported.
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  • 75
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    Applied physics 25 (1981), S. 31-34 
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    Keywords: 35 ; 42.55 ; 42.65
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    Notes: Abstract The decay rates of the3 D 1 level of I–II and the 3s 2 level of neon have been measured by the magnetic-field power dip method. The decay rate at the zero-pressure limit is found to be 7.1 MHz/2π for the3 D 1 level. The collision cross-section for excited I ions with helium atoms equals 0.19×10−15 cm2.
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  • 76
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    Applied physics 25 (1981), S. 49-56 
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    Keywords: 42.65 ; 78.20
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    Notes: Abstract Four-wave mixing with two circularly polarized counter-propagating waves inducing a helical birefringence structure can be used to measure a number of material parameters of a liquid crystalline medium. Application to a cholesteric substance is particularly interesting. A resonant effect is expected when the induced helix has a pitch coinciding with the natural helical pitch of the medium towards the isotropic → cholesteric transition. Field-induced shift in the transition temperature is also expected.
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  • 77
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    Applied physics 26 (1981), S. 185-190 
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    Notes: Abstract Optical frequency mixing through nonlinear mode coupling in a planar waveguide, fabricated with a cubic or uniaxial dielectric, is discussed. A threewave interaction is examined and the optimum crystal orientations that lead to the highest efficiency are determined in those particular cases in which they do not depend on the field distribution of the modes. The analysis is carried out in detail for cubic crystals; sensitivity to misalignments is also studied and numerical results are reported.
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  • 78
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    Applied physics 33 (1984), S. 1-7 
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    Keywords: 72.20 ; 42.65
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    Notes: Abstract Harmonic mixing of two alternating electric fields due to a Brownian charged particle in a nonlinear one-dimensional potential of cosine shape is investigated. The dynamics of the system are described by a time dependent Fokker-Planck equation. The appropriate distribution function is obtained by a matrix continued fraction expansion method, which is treated numerically. The dc signal due to mixing is computed for strong thermal fluctuations in all relevant parameter ranges of the pinning potential strength, damping and frequency. The dc signal without fluctuations is discussed separately. Resonance effects are shown in the electric dc field and the additional phase shift, caused by intrinsic relaxation processes.
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  • 79
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    Applied physics 14 (1977), S. 403-410 
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    Notes: Abstract The nonlinear optical susceptibility tensors of barium formate (point group 222) and magnesium barium fluoride (point group mm 2) have been determined by the method of Maker fringes on the basis of a more rigorous theoretical treatment of second-harmonic generation of electromagnetic waves in plane-parallel plates of optically biaxial crystals. The measurements have been carried out in comparison with the KDP standard at awavelength of 1.064 μm (Nd: YAG). Both crystals possess nonlinear coefficients smaller than KDP (d 36); they are phase matchable; magnesium barium fluoride exhibits a noncritical phase matching at a fundamental wavelenght of 1.04 μm.
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  • 80
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    Notes: Abstract The paper presents the results obtained in investigating the lineshape of two-photon absorption in the field of two spacially separated standing waves at the 3S–4D transition of Na. Measurements were carried out by using a CW dye laser.
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  • 81
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    Applied physics 15 (1978), S. 99-102 
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    Notes: Abstract Comparing the recombination light intensity produced in GaAs by a 1.06 μm pulse inducing two-photon absorption, with the intensity produced by a 0.53 μm pulse, we obtain directly the two-photon absorption cross-section. This method can be generalized to other materials.
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  • 82
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    Keywords: 79.70 ; 42.65 ; 85.60
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    Notes: Abstract In a series of recent experiments, research groups have made absolute frequency measurements with laser beams in the infrared region (μm) using a metal-metal point contact diode for the generation, frequency mixing and detection. At present there are two models which attempt to explain the rectification mechanism of the diode: 1) Tunneling of electrons through an intermediate oxide film from whisker to the metal base, i.e., configuration is considered to be a metal-oxide-metal (MOM) tunneling junction. 2) Rectification and nonlinear processes are the result of a thermal enchanced field emission. Such emission is a consequence of the immersion of the whisker in the laser radiation which results in conduction induced thermionic emission and/or generation of an electric field at the tip necessary for electron tunneling by field emission. The purpose of this comment is: a) to discuss qualitatively the basic difference between MOM and TFE theories as regards the origin of the nonlinearity and rectification properties of the metal point contact junction; b) to review the analyses describing the ultimate frequency response of the device; and 3) to provide a possible explanation for polarity reversal consistent with the TFE mechanism describing the operation of the whisker diode.
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  • 83
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    Applied physics 19 (1979), S. 39-41 
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    Notes: Abstract It is shown that when a distributed feedback dye laser is used to generate a train of picosecond pulses, the narrow lines observed in the spectrum are not longitudinal modes, but are due to the intrapulse refractive index changes caused by the heating effect of the pumping pulse.
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  • 84
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    Applied physics 19 (1979), S. 221-224 
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    Keywords: 42.10 ; 42.55 ; 42.65
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    Notes: Abstract Wave front of a light pulse is shown to be unstable as it propagates through a resonant saturable absorber, if its frequency is higher than the resonance frequency of the absorber. When ΔωT 2∼1, a small-scale transverse instability with the dimension of (λl abs)1/2 grows rapidly. Its growth-rate is of the order of the small-signal-absorption length of the medium.
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  • 85
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    Applied physics 19 (1979), S. 321-329 
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    Notes: Abstract A time-sinusoidal circularly polarized plane standing wave solution is obtained for isotropic lossless dielectric media with arbitrary nonlinearity. The spatial variation of the standing wave depends on the nonlinearity and is found by solving a problem of centralforce motion in which the electric complementary energy density furnishes the potential and the spatial coordinate has the role of time. Two special nonlinear dielectric response laws-cubic and quintic-are treated, and explicit solutions for the spatial variation of the wave amplitude and phase are obtained in terms of elliptic functions and elliptic integrals, respectively. The standing-wave solution is applied to give steady state solutions of two reflection/transmission problems (a) reflection from, or resonance modes between, ideally conducting planes and (b) reflection and transmission at a plane interface between two nonlinear dielectric media.
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  • 86
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    Applied physics 24 (1981), S. 45-48 
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    Notes: Abstract We investigated time-dependent effects related to the bistable operation of a CO2 laser with an intracavity nonlinear absorber (SF6). The response of the system to small perturbations was sensitively dependent on the operating laser line [P(12)→P(30)] of the 10.6 μm band. The narrow bistable region forP(12), due to a very narrow hysteresis loop, can be effectively utilized for optical switching, because of its pronounced sensitivity to variations in operational parameters. The maximum admissable beam blocking time (intracavity) for spontaneous return to lasing was measured forP(16), for a range of absorber pressures. This τm is related to the relaxation time of the upper level in the absorber.
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  • 87
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    Applied physics 24 (1981), S. 139-142 
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    Notes: Abstract The tuning and threshold behaviors of 5P 1/2–5P 3/2 stimulated electronic Raman scattering in In vapor were investigated. The Stokes output intensity was limited by atom depletion process in the atomic density available for the measurement. The anti-Stokes radiation observed was studied in terms of the phase matching condition.
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  • 88
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    Applied physics 24 (1981), S. 151-162 
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    Keywords: 32 ; 42.65
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    Notes: Abstract In this paper we consider the laser cooling of a trapped particle when the discrete nature of the quantum levels must be taken into account. We particularize the equations to the Lamb-Dicke limit when the oscillational, amplitude is much less than the optical wavelength. Then the quantum levels are coupled only to the neighbouring ones, and we can also find a small parameter to use for adiabatic elimination of rapidly varying terms. There emerges one rate equation for the probability distribution over the quantum states. The ultimate distribution is found to be of the Planckian type independently of the initial one. We solve the equation, generally and obtain the time evolution for an arbitrary initial distribution. In particular we look at an initially thermal, Poisson, or pure state distribution. For the thermal one we find that its shape is preserved during the cooling. The results are discussed.
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  • 89
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    Notes: Abstract We studied the change in Spin-flip Raman (SFR) gain and behaviour of the effectiveg-value as a function of pulsed electric fields inn-type InSb. The samples were held at 1.8 K in magnetic fields up to 1.4 T. Varying the strength of a pulsed electric field applied to the samples parallel to the magnetic field we found a direct correlation between the increase in electron temperature and the decrease of the Raman gain. Measurements of the Raman gain and spontaneous line width at different times after the starting of the electric pulse and during its fall time with a time resolution of 10 ns give no indication of a motional narrowing of the SFR line and of an increase of the gain during the decrease of the electric field pulse. These two predictions were made by Mooradian et al. (1972) to explain the observed transient increase of the intensity of the stimulated SFR Stokes radiation after an electric field across the sample was switched off. With our direct measurement of the Raman gain we could establish that at any time during and after the electric field pulse, the gain is less or equal to the value without electric field. In the electric field region from 0.3 V/cm up to 0.6 V/cm the Raman gain shows several maxima, originating from SFR scattering between different spin splitted conduction band levels. The electron distribution under pulsed electric field conditions give rise to a dynamically varying absorption mechanism of transmitted radiation. Time resolved transmission measurements explain the observed increase of stimulated SFR Stokes radiation during the switch-off time of electric field pulses by a lower absorption of radiation and not by a larger gain.
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  • 90
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    Applied physics 14 (1977), S. 377-380 
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    Notes: Abstract Due to spatial hole burning, standing-wave dye lasers require a large amount of selectivity inside the cavity for single-mode operation. The output power of these lasers is limited by losses caused by the frequency selecting elements. In a travelling-wave laser, on the other hand, spatial hole burning does not exist, thereby eliminating the need for high selectivity. A travelling-wave cw dye laser was realized by unidirectional operation of a ring laser, yielding single mode output powers of 1.2 W at 595 nm and of 55 mW in the UV-region with intracavity frequency doubling.
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  • 91
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    Applied physics 15 (1978), S. 53-57 
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    Keywords: 71.20 ; 42.65
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    Notes: Abstract In this paper we report on measurements of spin-flip-Raman gain inn-InSb as a function of the magnetic field. The measurements were carried out at temperatures of 1.8 K and 4.2 K and at a carrier concentration of 1.35×1015 cm−3. The Raman cross sections obtained from these results, e.g. 1.25×10−20 cm2/sr at a magnetic field of 10 kG and a pump frequency of 1884.35 cm−1, agree very well with those theoretically predicted by Wherrett and Wolland. Furthermore, these measurements yield line shapes and linewidths of the spontaneous scattering (100–1500 MHz) and allow the determination of the effectiveg-value with an accuracy known from ESR-investigations. These results are discussed in terms of already published theoretical investigations.
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  • 92
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    Applied physics 15 (1978), S. 319-322 
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    Notes: Abstract This paper reports on an experimental observation of coherent radiation after interaction with two standing-wave pulses having the time delayT in an absorbing rarefied gas. The radiation appears at the time 2T, 3T,... after the first pulse. The coherent radiation arises due to spacial transfer of polarization and to formation of a spacial polarization harmonic owing to a phase jump after two-photon interaction with the field of the second pulse. We observed intensity oscillations with frequency tuning of the exciting laser, varying the time delay between pulses.
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  • 93
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    Applied physics 17 (1978), S. 423-424 
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    Notes: Abstract An optical arrangement for studying two-photon absorption in liquids is presented. The main feature of this new arrangement is fuller utilization of fluorescence light. This makes possible application of very low power cw laser in such experiments.
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  • 94
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    Applied physics 14 (1977), S. 155-159 
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    Notes: Abstract We report for the first time stimulated magneto-Raman scattering inp-type InSb. Two different Raman scattering processes were observed. The first one has a Raman shift of about 2cm−1/kG and is observed at magnetic fields up to 30kG. The other one is observable only at high magnetic fields above 30kG and shows Raman shifts between 1.2cm−1 and 3.0cm−1 with a tuning rate of about 0.2cm−1/kG. The first process can be interpreted either as spin-flip Raman scattering by photo-excited electrons in the conduction band or as Raman scattering by holes in the valence band involving transitions from heavy to light hole states. The other Raman shift observed seems to occur on account of transitions between the heavy hole ladders.
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    Applied physics 17 (1978), S. 393-400 
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    Notes: Abstract Stimulated Raman scattering by polaritons when employing a nonlinear crystal inside the cavity of the laser with Q-switching and locked to fundamental frequency was theoretically studied. The equations were formulated describing the dynamics of the fundamental, Stokes and polariton waves under the assumption of instant Q-switching and uniformity of radiation except in the longitudinal direction. Numerical solutions of the equations were found and analysed. We demonstrate the influence, on generation characteristics, of the most important parameters, such as the effective nonlinearity, the initial level of population inversion, the feedback of the Stokes wave and the group mismatch between a Stokes and a pump wave. Optimum generation conditions are determined. Possibilities of the method are discussed for the generation of a) giant pulses which are controllable with regard to carrier frequency and duration but are unachievable with other methods, b) Stokes pulses of very small duration and high energy having sharp trailing edges, and c) analogous polariton pulses in the middle and far infrared range. The generation using a number of polariton branches in LiNbO3 was considered as an example. Calculations are in qualitative agreement with experimental data.
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    Applied physics 18 (1979), S. 271-274 
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    Keywords: 42.65 ; 64 ; 77.80
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    Notes: Abstract The temperature-dependent optical second-harmonic generation in thermally depoled La-doped lead zirconate titanate (PLZT) ceramics of composition 8/65/35 and 9/65/35 has been studied. A microscopic model for the anomalous phase transition behaviour of these compounds is suggested.
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    Applied physics 17 (1978), S. 211-232 
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    Notes: Abstract Physical principles, new ways and means of creation, schemes, characteristics and features of efficient high-power tunable pulse Raman lasers, operating in the near and middle ir are reviewed. The paper includes: tunable dye and Nd lasers as pump sources; promising active media and their optimal excitation methods; optical systems for producing spatially homogeneous pumping; the physics of Raman oscillators and their practical schemes, efficient high pulse energy liquid N2 and compressed H2 Raman oscillators, covering several bands in the range between 1.4 and 9.2 μm; the physics and construction of efficient tunable Raman amplifiers-convertors, amplifying in the saturation regime of spontaneously scattered or beforehand produced and collimated external Stokes signals, obtained in the spectral range between 0.83 μm and 18 μm. Raman laser using a, so-called, broadband pump where the linewidth of pumping light is broader than the spontaneous scattering linewidth, are also discussed. Features of both amplification and oscillation regimes of such broadband pumped Raman lasers are reported, and conditions for the efficient frequency conversion are determined.
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    Applied physics 24 (1981), S. 303-306 
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    Notes: Abstract This paper describes the experimental investigation of stimulated Raman scattering obtained from a multimode fiber. 10 orders of stimulated Stokes scattering of wavelengths in the 546–702 nm region were obtained from a 480m multimode, low-loss, graded-index quartz fiber pumped by a 532 nm frequency-doubled YAG-Nd laser beam with a pulse duration of 7 ns, output power of 0.7 MW and repetition rates of 5 and 10 pps.
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    Applied physics 18 (1979), S. 177-181 
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    Notes: Abstract We have studied experimentally stimulated Raman scattering and 4-wave-interaction processes occuring in hydrogen gas, which is excited by a Nd:YAG-pumped dye laser. The tuning ranges of the various Stokes and anti-Stokes lines, which are generated with high efficiency, cover the spectrum from 185 to 880 nm without a gap.
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    Applied physics 20 (1979), S. 319-323 
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    Keywords: 33 ; 42.65 ; 42.80
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    Notes: Abstract The suitability of a singly resonant optical parametric oscillator pumped by a one-mode field and oscillating simultaneously in several signal and idler modes, for intracavity absorption spectroscopic measurements is studied theoretically. For steadystate operation, the enhancement factor ξ indicating the increased detection sensitivity, is shown to be mainly determined by the ratio of the intensity in one of the signal modes to the intensity (per mode) due to parametric fluorescence. Hence, rather high values of ξ, say of order 108 or more, might be attainable, at least in principle. For pulsed operation, on the other hand, a numerical analysis leads to the result that for realistic pulse durations only moderate values of ξ (smaller than some 103) will be found.
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